A standard hydraulic hammer or chipper has a housing, a tool axially reciprocal in the housing and engageable with a workpiece, a piston axially reciprocal in the housing and having a front face engageable with the tool to drive it against the workpiece, and an automatic distributor valve which alternately pressurizes and depressurizes front and back chambers of the normally double-acting piston to reciprocate it axially against the tool. The distributor valve is fed with hydraulic fluid at a generally constant pressure.
When the material being hammered is hard, stone for instance, best penetration is achieved by reciprocating the tool slowly and striking the piston against the tool with great force. Contrarily, when the material is soft it is advisable to use a succession of less powerful but more frequent blows.
The frequency with which the hammer piston reciprocates is largely a function of the pressure that is applied to it on the forward stroke. This pressure is typically adjustable by means of a pressure-control valve connected right in the housing between the incoming hydraulic line and the reversing valve. With a double-acting assembly the return pressure or the counter pressure is easily adjusted to slow or speed up the reciprocation of the piston. Thus a standard configuration for such a hammer or scaler has a simple adjustment knob or the like which is regulated by the user according to work conditions.
In another type of system described in French patent 2,375,008 a remote pneumatic or electrohydraulic control system works with a plurality of different feed openings in the hammer piston's chamber to vary the frequency of the hammer blows by varying the stroke length. The force with which the piston strikes is increased as the stroke length increases. Such a device must be set by the user in accordance with instantaneous work conditions.